The present disclosure relates to a development device that is used in an image forming apparatus, such as a copying machine, a printer, a facsimile machine or a multifunctional machine thereof, which utilizes an electrophotographic method and an image forming apparatus that includes such a development device. More particularly, the present invention relates to a development device that supplies a two-component developer composed of a toner and a carrier and that discharges the excess developer and an image forming apparatus that includes such a development device.
In an image forming apparatus, a latent image that is formed on an image carrying member composed of a photosensitive member and the like is developed with a development device so as to be visualized as a toner image. In one of such development devices, a two-component development method using a two-component developer is adopted. In this type of development device, the two-component developer (hereinafter also simply referred to as a developer) composed of a carrier and a toner is stored within a development container, a development roller that supplies the developer to an image carrying member is provided and an agitation member is also provided that supplies the developer within the development container to the development roller while transporting and agitating the developer.
Although in this development device, the toner is consumed by the development operation, the carrier is left within the development device without being consumed. Hence, the carrier which is agitated together with the toner within the development container is degraded as the frequency of agitation is increased, with the result that the charging performance of the carrier for the toner is gradually lowered.
Hence, a development device is known in which a developer containing a carrier is supplied into a development container and in which the excess developer is discharged such that a decrease in charging performance is reduced.
For example, a development device is known in which in a system for supplying a carrier and a toner into a development container, an agitation member includes: a first transport portion that transports a developer within the development container; a second transport portion that is provided on the downstream side of the first transport portion in a transport direction and that is formed with a spiral blade which transports the developer in a direction opposite to the first transport portion and which is faced oppositely; a disk portion (damming member) that is provided on the upstream side of the second transport portion in the transport direction; and a third transport portion that is provided on the upstream side of the disk portion in the transport direction of the second transport portion, that transports the developer in the same direction as the first transport portion and that discharges the developer from a developer discharge port.
In the development device including the first transport portion, the second transport portion and the third transport portion, when the developer is supplied into the development container, by the rotation of the first transport portion, the developer is transported to the downstream side of a transport chamber while being agitated. When the opposite spiral blade of the second transport portion is rotated in the same direction as the first transport portion, a transport force in a direction opposite to the transport direction of the first transport portion is applied to the developer. By the transport force in the opposite direction, the developer is dammed to become bulky, and thus the excess developer is passed over the second transport portion and the disk portion (damming member), is moved to the developer discharge port and is discharged to the outside.
Conventionally, a development device is known which includes, as an agitation member for agitating and transporting a developer, a first transport portion that transports the developer and a disk portion (damming member) that is provided on the downstream side of the first transport portion in a transport direction and that dams the developer transported by the first transport portion. In such an agitation member, a rotation shaft may be used which includes a large shaft diameter portion that is provided in the first transport portion, a small shaft diameter portion that is smaller in diameter than the large shaft diameter portion and a shaft diameter change portion that is arranged in a boundary between the large shaft diameter portion and the small shaft diameter portion.